Light control film

ABSTRACT

A light control film having a refractive index n and an uneven, irregular surface pattern provides a reasonable level of light diffusion without a glare problem provided, for any cross-section perpendicular to the base plane of the film, the average of absolute values of slope θ ave  of a curve along the edge of the cross-section contoured by the rough surface pattern (profile curve) is at least 78-34 n  degrees and no higher than 118-34 n  degrees, or the average of absolute values of slope θ ave  of a profile curve to the length L1 of a straight line defined by the intersection of the base plane and the cross-section satisfies the following formula (3) or (4) for substantially all cross-sections.
 
θ ave   ÷Lr×n   2 ≧40  (3)
 
50≦θ ave   ×Lr×n   2 ≦135   (4)

FIELD OF THE INVENTION

The present invention relates to a light control film used for abacklight of liquid crystal displays etc., and a backlight using thesame.

RELATED ART

A backlight of an edge-light, in which a light source is located atleast on one end of a light guiding plate, is widely used as a backlightfor liquid crystal displays etc. An edge-light backlight has suchadvantage that the thickness of the backlight itself can be reduced.However, as a light source is located on the edge, an emergent lightcontains much components leaning greatly away from the front direction,thereby making it difficult to attain a high front luminance. Inconventional backlights, a plural number of optical films and lightdiffusion films, including prism sheet, are used in combination in orderto orient the emergent light to the front, and thus to improve a frontluminance (Examples: The Japanese Patent Application Laid-Open No.8-55507 and the Japanese Patent Application Laid-Open No. 2000-352607etc.).

However, such backlight, in which multiple sheets of optical films areincorporated, had difficulties in reducing the thickness and loweringthe cost, and was faced by unfavorable problems such as generation ofthe Newton rings attributable to the lamination of multiple opticalfilms and scars caused by the contact of films.

On the other hand, prism sheets and lens sheets are widely used as alight control film for controlling the direction of an emergent light.However, since these optical films are expensive in general, a lightcontrol film has been developed as an alternative, offering variousproposals on the surface geometry and rough surface (unevenness)patterns of the film. For example, Japanese Patent Application Laid-OpenNo. 4-146401 proposes a material with irregular rough surface patterns,which are produced by combining sawtooth elements of various sizes, as acontrolling material to be used in combination with light diffusionmaterial. The Japanese Patent Application Laid-Open 05-169015 alsoproposes a light diffusion sheet, in which many optical elements ofcertain shape, such as hemispheric, conical or prismatic shape, areregularly arranged in a certain pitch.

However, although the conventional light control films containing prismsheet or lens sheet can be designed based on geometrical optics forincreasing the ratio of the light emerging towards the front (the planeorthogonally crossing the film surface), regularly arranged protrusionsare likely to generate interference patterns, thus causing glare andpoor visibility when this film is used alone. While solving thesedisadvantages requires the use of light diffusion sheets etc., togetherwith a light diffusion film, the use may cause above-mentioned problemsattributable to the lamination of the films and the reduced luminance ingeneral.

Further, if an irregularly uneven surface is produced by the combinationof sawtooth elements of various sizes as in a controlling materialdescribed in the Japanese Patent Application Laid-Open No. 4-146401, itis not easy to provide uniform characteristics such as higher luminanceand less glare over the entire film surface.

Accordingly, an object of the present invention is to provide a lightcontrol film, which has an improved front luminance and a proper amountof diffusiveness and has no glare problem when it is used alone or incombination with a small number of optical films. Further, anotherobject is to provide a light control film without dispersion (variance)of the characteristics.

DISCLOSURE OF THE INVENTION

The inventor of the present invention conducted various studies, toachieve the foregoing object, on various factors which define thesurface geometry of a light control film, including the geometry ofsurface roughness, slope to the film surface (base plane), height andpitch of protrusion and recess, etc. As a result, he found that anincident light could be effectively oriented towards the front directionof the film (emergent direction) by appropriately controlling the slopeof the rough surface patterns to the film surface, and that the frontluminance could be improved by the use of a fewer number of opticalfilms. More specifically, he found that, as shown in FIG. 1, excellentfront luminance could be achieved when the average of the absolute valueof slope (θ_(ave)) of a curve (profile curve) 101 contouring the edge ofthe cross section 100, which is a cross section in any directionperpendicular to the film surface (the surface opposite to the surfacewith the rough surface patterns), is within a certain range. Further, hefound that by using the average of absolute values of slope (θ_(ave))(degree) of the profile curve 101 as an indicator of the slope of theunevenness and the ratio (Lr=L2/L1) of the length of the profile curve(L2) to the length (L1) of the straight line 102 determined by anintersection of the film surface and the cross section as an indicatorof the height of the unevenness, changes in the front luminance could bedescribed by a particular formula expressing a correlation with theindicators and that the excellent front luminance could be achieved whenthis value is within a certain range. Thus, he accomplished the presentinvention.

In other words, the light control film of this invention is the lightcontrol film having rough surface patterns, wherein regarding any crosssection perpendicular to the base plane of the film, an average ofabsolute values of slope (θ_(ave)(degree)) of a curve along the edge ofthe cross section contoured by the rough surface (the curve is referredas a profile curve hereinafter) to said base plane is 20 degree orhigher and 75 degree or lower over substantially all cross sections.(Hereinafter, the slope of a profile curve for the rough surfacepatterns at 20≦θ_(ave)≦75 is defined as Condition 1)

Further, the light control film of the present invention is the lightcontrol film having a rough surface patterned layer made of materialwith a particular refractive index n, wherein regarding any crosssection perpendicular to the base plane of the film, an average ofabsolute values of slope (θ_(ave)(degree)) of a curve along the edge ofthe profile contoured by the rough surface pattern (profile curve) tosaid base plane is 78-34 n degree or higher and 118-34 n degree or lower(Hereinafter, the slope of a profile curve for the rough surface patternat (78-34 n)≦θ_(ave)≦(118-34 n) is defined as Condition 2).

In the light control film of the present invention, the difference ofthe average of absolute values of slope of the profile curve, dependingon the direction of the profile including the profile curve, ispreferably 30 degrees or less.

Further, the light control film of this invention is the light controlfilm having rough surface patterns, wherein regarding any cross sectionperpendicular to the base plane of the film, an average of absolutevalues of slope (θ_(ave)(degree)) of a curve of the edge of the profilecontoured by the rough surface patterns (profile curve) to said baseplane and the ratio (Lr=L2/L1) of the length of said profile curve (L2)to the length (L1) of the straight line determined by an intersection ofsaid base plane and the cross section satisfy, over substantially allcross sections, Formula (1) or Formula (2) as described below(Hereinafter, the condition to satisfy Formula (1) or Formula (2) isdefined as Condition (3).θ_(ave) ÷Lr≧20  (1)25≦θ_(ave) ×Lr≦60  (2)

The light control film of this invention is the light control filmhaving a rough surface patterned layer made of material with a certainrefraction index n, wherein regarding any cross section perpendicular tothe base plane of the film, an average of absolute values of slope(θ_(ave)(degree)) of a curve along the edge of the profile contoured bythe rough surface pattern (profile curve) to said base plane and theratio (Lr=L2/L1) of the length of said profile curve (L2) to the length(L1) of the straight line determined by an intersection of said baseplane and the cross section satisfy, over substantially all crosssections, Formula (3) or Formula (4) as described below (Hereinafter,the condition for the slope of the profile curve of the rough surfacepattern to satisfy Formula (3) or Formula (4) is defined as Condition4).θ_(ave) ÷Lr×n ²≧40  (3)50≦θ_(ave) ×Lr×n ²≦135  (4)

In this invention, the base plane of the film means the surface thereof,if the film is deemed as substantially flat surface, whereas if thesurface opposite to the surface with the rough surface pattern of thelight control film of this present invention is a smooth surface, thissmooth surface is deemed as a base plane. Further, if this oppositesurface is uneven rather than smooth, the surface including a centerlineof these two different directions can be deemed as a base plane.

Such slope of a profile curve to the base plane can be obtainedgenerally as f′(x) by differentiating f(x) by x, where the profile curvey is expressed as y=f(x), while the average (S_(ave)) of its absolutevalues is expressed by the undermentioned Formula (5), where the lengthof the section for which the abovementioned value is calculated isdefined as L. The average of absolute values of slope (θ_(ave))expressed in angle can be expresses by the Formula (6) below.

$\begin{matrix}{S_{av} = {\frac{1}{L}{\int_{0}^{L}{{{f^{\prime}(x)}}{\mathbb{d}x}}}}} & (5) \\{\theta_{av} = {\frac{1}{L}{\int_{0}^{L}{{{\tan^{- 1}{f^{\prime}(x)}}}{\mathbb{d}x}}}}} & (6)\end{matrix}$

Although these functions can be used in product design, it is difficultto express a profile curve for actual products with a general function,and to obtain the average of absolute values of slope. Therefore, inthis present invention, the value obtained as described below is definedas an average of absolute values of slope of a profile curve.

First of all, a profile curve is measured, by using a surface profiler,from any point on the surface with rough surface patterns in anydirection. Measurement results are composed of height data of thesurface (h(d₁), h(d₂), h(d₃) . . . h(d_(m))) measured at the pointsarranged at particular intervals (Δd) in a cross sectional direction(d₁, d₂, d₃ . . . , d_(m)). For example, these data are expressed in agraph, where the height of the rough surface pattern and the directionof a profile curve are displayed on the vertical and horizontal axis,respectively, as shown in FIG. 2. The segments of the profile curvedivided by an interval (Examples: (a-b), (c-d) . . . ) can be deemed asa straight line if the interval is sufficiently short, where theabsolute value of slope θi (i=1, 2, 3 . . . m) (Unit: degree) can beexpressed with the following formula.θi=tan⁻¹ {[h(d _(i))−h(d _(i−1))]/Δd}  (7)

The average of the abovementioned slope obtained for all segments of theprofile curve divided by a certain interval (Δd) is defined as theaverage of absolute values of slope, θ_(ave).

$\begin{matrix}{\theta_{ave} = {\frac{1}{m}{\sum\limits_{i = 1}^{m}{\theta_{i}}}}} & (8)\end{matrix}$

The length of the abovementioned interval (Δd) is long enough to be ableto accurately reflect the geometry of the rough surface patterncontained in the profile curve, specifically about 1.0 μm long or less.Further, the level of preciseness differs depending on a surfaceprofiler used in the measurement of the profile of the film having roughsurface patterns. In the light control film of this present invention,Conditions 1 and 2 are applied to the figures obtained by using a stylusprofiler. As it is considered that the effect of measurement device usedcan be removed by operation on measurement values, Conditions 3 and 4are applied regardless of the measurement device.

In the light control film having such a rough surface pattern of thispresent invention, of the light entering from the opposite onto thesurface with such a rough surface pattern and emerging from the surfacewith the rough surface pattern, the components within the emergent angleranging from 0 to 30 degrees can be increased, thereby attaining thefront luminance that is equal to or higher than that attained by a prismsheet. Moreover, said light control film has a proper amount of lightdiffusiveness and generates neither glare nor interference patterns.

Further, the light control film of this present invention has the roughsurface pattern satisfying either of the abovementioned Conditions 1-4,wherein the average of absolute values of slope (θ_(ave)) of the profilecurve increases gradually as its direction approaches from the firstdirection, which is parallel to the base plane of said light controlfilm, to the second direction which is parallel to the base plane ofsaid light control film and perpendicular to said first direction.

In this light control film, when it is located on a backlight such thatthe longitudinal direction of the light source of the backlight shouldbe along the first direction, changes in angular dependence of luminanceof backlight (hereinafter angular dependence of luminance) due todifference in the direction to the light source can be corrected toattain uniform luminance.

The light control film of this present invention has a rough surfacepattern satisfying either of the aforementioned Conditions 1 to 4,wherein the slope of the profile curve to the base plane graduallyincreases or decreases when approaching from one end to the other end ofthe film.

In this light control film, when the side of a light source of abacklight is located to represent an end of the film, changes in angulardependence of luminance due to difference in the distance from the lightsource can be corrected to attain uniform luminance.

The backlight device of this present invention is the backlight deviceusing the aforementioned light control film of this present invention.Specifically, this backlight device is a backlight device comprising alight guiding plate, which has a light source at least on one end and alight emergent surface almost orthogonally crossing said end, and alight control film located on the light emergent surface of said lightguiding plate, or a backlight device comprising a light control film, alight diffusion material and a light source on the side opposite to thelight emergent surface of the light control film, in this order.

According to this present invention, a light control film having a highfront luminance and a proper amount of light diffusiveness can beprovided. Further, the backlight device of this present invention canminimize, by the use of such light control film, other materials to beused in combination with this film, thereby reducing the thickness ofthe backlight device. It can also control the occurrence of interferencepatterns and the generation of scars due to contact of films.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows illustrative views of a rough surface pattern of the lightcontrol film of this invention.

FIG. 2 is an illustrative view of a profile curve of the light controlfilm of this invention.

FIG. 3 illustrates cross sectional views of the light control filmsaccording to embodiments of this invention.

FIG. 4 shows an example of a 3-dimensional rough surface pattern usedfor simulating differences in emergent angle characteristics accordingto the pattern.

FIG. 5 shows the result of 3-dimensional simulation.

FIG. 6 shows the results of 3-dimensional simulation.

FIG. 7 shows the results of 3-dimensional simulation.

FIG. 8 shows the results of 3-dimensional simulation.

FIG. 9 shows a location at which the luminance of the backlight ismeasured.

FIG. 10 shows distributions of emergent angles at different measurementlocations or at different directions of emergent angle measurement tothe light source, where (a) is a distribution of emergent anglesmeasured at the center of the film in a direction parallel to the lightsource, (b) is a distribution of emergent angles measured at the centerof the film in a direction perpendicular to the film, and (c) is adistribution of emergent angles measured not at the center of the filmbut closer to the light source in a direction perpendicular to the lightsource.

FIG. 11 illustrates a profile curve of a light control film capable ofcorrecting emergent angle distribution dependency on the distance fromthe light source.

FIG. 12 illustrates a profile curve of a light control film capable ofcorrecting emergent angle distribution dependency on the distance fromthe light source.

FIG. 13 is a perspective view showing an example of rough surfacepatterns of a light control film of this invention.

FIG. 14 shows a backlight device of this invention according to anembodiment of this invention.

FIG. 15 shows a backlight device of this invention according to anotherembodiment of this invention.

FIG. 16 shows a luminance distribution of a light control film accordingto an embodiment of this invention.

FIG. 17 shows a luminance distribution of a light control film of thecomparative example.

PREFERRED EMBODIMENT OF THE INVENTION

The light control film and the backlight device of this invention willbe explained in detail with reference to drawings. Sizes (thickness,width, height etc.) of each component in the drawings used forexplaining the present invention have been enlarged or reduced in linewith the requirements for explanation, and do not reflect exact size ofeach component of an actual light control film and a backlight device.

FIGS. 3( a)-3(c) are schematic views showing light control films 10according to embodiments of the present invention. As illustrated inthese figures, the light control film 10 of the present invention has arough surface pattern made of fine protrusions and recesses on one sideof an almost flat film, with distinctive characteristics in the geometryof this rough surface pattern. The rough surface pattern may be formed,as shown in FIG. (a) and FIG. (b), on a layer 12 formed on one side ofthe film used as a substrate 11. Alternatively, as shown in FIG. (C) thelight control film may be comprised of only the layer 12, on which therough surface pattern is formed.

The light control film of this invention controls the direction ofincident light so that the component of the emergent light directinginto a certain range of angles from the front when the light incidentfrom the opposite side of the rough surface patterned surface emergesfrom the rough surface patterned surface increases, thereby enhancingthe front luminance and providing light diffusiveness for preventing theoccurrence of glare. The opposite side of the rough surface patternedsurface is typically a smooth surface, but is not limited to a smoothsurface. For example, the opposite surface can be matted ordot-patterned.

Conditions of the rough surface pattern for controlling the direction oflight mentioned above will be explained.

Conditions 1 and 2

The inventor of the present invention firstly assumed a profile curvecomprising multiple patterns of uniform protrusions for a segment of acertain length of a profile curve, then conducted simulation of therelationship between incident light and emergent light by changing thegeometry and height of the pattern, the angle of incident light etc.,and examined conditions for obtaining an optimal emergent light. In thesimulation, it is assumed that, as incident and emergent lights, a lightgoes from one side of the profile curve to other side within the surfacecontaining the profile curve, and a refraction index of 1.5, an indexfor ordinary acrylic resin, is used for one side and a refraction indexof air for other side in calculation. Further, it is assumed that thedistribution of incident lights is same with the distribution ofemergent lights from a light guiding plate of an actual backlight(distribution of emergent lights passing through the center of a lightguiding plate and orthogonally crosses the light source).

Such simulation revealed that by restricting the average of absolutevalues of slope (average slope) (θ_(ave)(degree)) to a segment of aprofile curve to 20 degrees or higher and 75 degree or lower, the lightleaning greatly from the front direction could be effectively orientedto the front direction, thereby the front luminance could be improved.This average slope (θ_(ave)(degree)) is preferably 25 degrees or higherand 60 degrees or lower, and more preferably 30 degrees or higher and 50degree or lower, to obtain particularly excellent effects.

These conditions need to be satisfied for substantially all crosssections. “To be satisfied for substantially all cross sections” meansthat the condition needs to be satisfied for most of the cross sectionsof a particular light control film observed, but a few cases whichcontain one or two cross sections which do not satisfy the condition maybe included. For example, said conditions may not be satisfied due to afewer number of rough surface patterns (protrusions) for the crosssection at the edge of the light control film, while it is consideredthat the conditions of this invention are satisfied if theaforementioned conditions are satisfied for a relatively long profilecurve.

Meanwhile, the abovementioned simulation for identifying conditions tobe satisfied by the rough surface pattern of this invention assumes amaterial whose refraction index on the incident side of the protrusionpattern is 1.5. However, the rough surface pattern of the light controlfilm of this invention can be made with the material generally used inthe optical film, without limiting its refraction index to 1.5. In thegeneralization by taking the refraction index n into account,abovementioned effects are obtained with the average slope(θ_(ave)(degree)) is (78-34 n) degrees or higher and (118-34 n) degreesor lower.

By designing the geometry of the rough surface pattern taking account ofthe refraction index of the material with which the pattern is made, theluminance in the front direction can be further improved.

Conditions 3 and 4

Conditions 3 and 4 have been obtained based on the results of3-dimensional simulation. In other words, the inventor of this inventionsimulated the relationship between incident light and emergent light bychanging the shape and height of the pattern, the angle of the incidentlight etc., for a single protrusion pattern made of a rotating body,which is made by rotating around the axis z a curve 401 drawn on thesurface orthogonally crossing the xy plane, as a base plane, as shown inFIG. 4, and examined the conditions for obtaining an optimal emergentlight. Then, the distribution of lights emerging from the protrusionpatterned side (angular characteristics of emergent light) when thelight with the same distribution with that of the light emerging from alight guiding plate of an actual backlight enters from the bottom ofthis protrusion pattern was found by calculation. In the calculation,refraction index of 1.5, an index for common acrylic resin, was used asa refraction index n inside the protrusion pattern.

FIG. 5 shows the distribution 501 of emergent light, a result obtainedby the simulation in respect of the pattern having the geometry shown inFIG. 4. A dotted line in FIG. 5 represents a distribution 502 ofincident light. In order to attain good front luminance and a certainextent of light scattering, it is desirable that the emergent lightcontains a higher ratio of light components emerging into the range of±30 degrees from the front (0 degree) and has high uniformity in therange of ±30 degrees from the front (0 degree).

Then, in order to find conditions for obtaining the angularcharacteristics satisfying the above conditions with regard to the roughsurface on which multiple protrusion patterns are formed, changes in thedistribution of emergent light due to various changes made to the shapesand the height of the pattern was simulated with respect to the systemhaving multiple abovementioned protrusion patterns. Results of thesimulation are shown in FIG. 6, where a horizontal axis represents theaverage slope (θ_(ave)) of the curve for the whole of the multipleprotrusion patterns, and a vertical axis represents energy of emergentlight. The first group 601 represents the emergent light within therange of 6 degrees around the axis z (hereinafter emergent light₆), thesecond group 602 represents the emergent light within the range of 18degrees around the axis z (hereinafter emergent light₁₈) and the thirdgroup 603 represents the emergent light within the range of 30 degreesaround the axis z (hereinafter emergent light₃₀).

The results of this simulation show the tendency that the ratio of theemergent light 30 increases as the average slope (θ_(ave)) increases,but begins to decrease after a certain point. Studies conductedaccordingly to find a comprehensive indicator regarding the geometry ofsurface roughness which is correlated with the emergent light 30revealed that the correlation with the emergent light 30 can be bestdescribed by using a quotient between or the product of the averageslope (θ_(ave)) and the ratio of the length of the curve (L1) to thelength of the bottom of the curve 401 (Lr=L2/L1, hereinafter “curvelength ratio”).

FIGS. 7 and 8 show the results of simulation. FIG. 7 shows changes inenergy of emergent light, where the vertical axis represents the valuesobtained by dividing the average slope (θ_(ave)) by the curve lengthratio (Lr). FIG. 8 shows changes in energy of emergent light, wherehorizontal axis represents the values obtained by multiplying theaverage slope (θ_(ave)) by the curve length ratio (Lr).

The results of these simulations reveal that when the value obtained bydividing the average of absolute values of slope (θ_(ave)) of the curveby the curve length ratio (Lr) (quotient) is 20 or higher, and when thevalue obtained by multiplying the average of absolute values of slope ofthe curve (θ_(ave)) by the curve length ratio (Lr) (product) is 25 orhigher but 60 or lower, the energy of emergent light within the range ofemergent angle of 30 degrees markedly increases. As the rough surfacepattern formed on the film surface can be considered as the assembly ofmultiple protrusion patterns, aforementioned relationship can be appliedto the rough surface pattern formed on the film surface. Accordingly, itshould be understood that a light control film with a high frontluminance and a proper light diffusive property can be formed bysatisfying the undermentioned condition (Formula (1) or Formula (2)).θ_(ave) ÷Lr≧20  (1)25≦θ_(ave) ×Lr≦60  (2)where, θ_(ave) is the average of absolute values of slope to thereference plane of the profile curve contoured by the rough surfacepattern regarding an arbitrary cross section perpendicular to the baseplane of the film and Lr is the ratio of the length (L2/L1) of astraight line (L1) drawn by intersection of the base plane and the crosssection to the length of a profile curve (L2).

Further, the value obtained by dividing the average (θ_(ave)) by thecurve length ratio (Lr) in Formula (1) is more preferably 25 or higher,while the value obtained by multiplying the average slope (θ_(ave)) bythe curve length ratio (Lr) in Formula (2) is more preferably 35 orhigher and 50 or lower.

Condition 3 needs to be satisfied for substantially all cross sections.“To be satisfied for substantially all cross sections” means that thecondition needs to be satisfied for most of the cross sections of aparticular light control film observed, but a few cases which containone or two cross sections which do not satisfy the condition may beincluded. For example, said conditions may not be satisfied due to afewer rough surface patterns for the cross section at the edge of thelight control film, while it is considered that the conditions of thisinvention are satisfied if aforementioned conditions are satisfied for arelatively long profile curve.

Aforementioned 3-dimensional simulation assumes the protrusion patternsmade of the material with the refraction index of 1.5. However, therough surface pattern of the light control film of this invention canemploy material used generally in optical film, the refraction index ofwhich is not limited to 1.5. By taking the refraction index n intoaccount, the aforementioned formulas (1) and (2) can be generalized asfollows:θ_(ave) +Lr×n ²≧40  (3)50≦θ_(ave) ×Lr×n ²≦135  (4)

Further, the value of Formula (3) is more preferably 50 or higher, whilethe lowest value and the highest value of Formula (4) are morepreferably 70 or more and 115 or less, respectively. By designing thegeometry of the rough surface pattern by taking the refraction index ofthe material composing the rough surface pattern into account, theluminance towards the front can be further improved.

The light control film of this invention is able to attain a high frontluminance and a certain extent of light diffusiveness by designing roughsurface patterns to satisfy the aforementioned conditions. The lightcontrol film of this invention having such characteristics can be usedas a film for controlling the direction of emergent light by placing thefilm directly on, for example, a light guiding plate of an edge-lightbacklight device or above the light source of a direct backlight devicevia a light diffusion plate.

Additional Conditions

Further, it is preferable that, in the light control film of thisinvention, the average slope (θ_(ave)) of rough surface patterns ischanged by taking account of the relationship with the location of alight source of a backlight device. Regarding the relationship with thelight source, when a long and narrow light source is located at one endor both opposite ends of a backlight, the angle to the longitudinaldirection of the light source and the distance from the light sourceneeds to be taken account.

Regarding the angle to the longitudinal direction of a light source,when angular dependence of luminance of emergent light of backlight(angular dependence of luminance) is measured, at almost all measurementpoints the luminance at the emergent angle leaning greatly from thefront tends to become higher in general as the measurement directionmoves from parallel to perpendicular to the longitudinal direction ofthe light source. For example, when the luminance at the emergent angleis measured at the center point C in direction parallel to the lightsources 91 and 92 (x direction in FIG. 9) in the backlight in whichlight sources 91 and 92 are located on two parallel ends of the lightguiding plate 90 as shown in FIG. 9, a uniform luminance in the widerange of emergent angle as shown in FIG. 10( a) is obtained at mostmeasurement points. On the other hand, when the luminance at theemergent angle is measured at the point C in direction perpendicular tothe light sources 91 and 92, the luminance at large emergent anglestends to be higher as shown in FIG. 10( b). Such tendency is conspicuousin an edge-light backlight, while it is also seen in a direct backlightin which the part of the light diffusion material corresponding to thelight source is dot-patterned.

In order to correct difference in such angular dependence of luminanceof the backlight, it is preferable that the average slope of a profilecurve in the light control film of this invention is made larger as thedirection of the cross section becomes from parallel to perpendicular tothe light source. By doing so, the light leaning greatly from the frontcan be oriented to the front, thereby increasing the front luminance.

It is preferable that the condition (hereinafter Condition 5) forcorrecting difference in the angular dependence of luminance of thisbacklight are satisfied by a profile curve on the cross section assumedin any direction from any point on the film, and regardless of thedirection of the cross section, either of aforementioned Conditions 1-4needs to be satisfied. In order for the rough surface pattern to satisfyeither of aforementioned Conditions 1-4, and Condition 5, which requiresgradual increase of the average slope of substantially all profilecurves depending on the angle of the cross section to the longitudinaldirection of a light source, every single protrusion pattern composingrough surface patterns should be shaped to satisfy Condition 5. In otherwords, by shaping the cross section parallel to the bottom in theprotrusion pattern shown in FIG. 4 not as a complete round shape but anoval shape, whose axis becomes shorter as it moves from the directionparallel (x-axis direction, for example) to perpendicular (y-axisdirection, for example) to the longitudinal direction of a light source,this pattern is able to have an anisotropic property due to therelationship between the slope of a profile curve and the light source.

With respect to the distance from a light source, if angular dependenceof luminance of luminance in the direction perpendicular (direction y inFIG. 9) to the direction of a light source is measured, the luminance atthe emergence angle leaning greatly from the front tends to be higher asthe measurement point is closer to the light source. For example, FIG.10(C) shows the luminance at the emergent angle perpendicular to thelight source 91 when it was measured at point F, which is closer to thelight source 91 on one end, rather than to the center point C of thelight guiding plate shown in FIG. 9. In order to correct such angulardependence of luminance, which depends on the distance from a lightsource, the slope is increased or decreased gradually depending whetherthe slope plane of the rough surface pattern is on the side of the lightsource or on the opposite side of the light source. Specifically, if theslope plane is on the side of the light source, the slope is increasedas it approaches closer to the light source, while if the slope plane ison the opposite side of the light source, the slope is decreased as itapproaches closer to the light source. The abovementioned conditions ofchanging slope according to the distance from the light source need notto be satisfied by all adjacent protrusions in the rough surfacepattern, but need to be satisfied only by the average slope of roughsurface patterns contained in the segments formed by dividing a profilecurve with an appropriate interval. This is shown in FIG. 11 and FIG.12.

FIG. 11 shows the case in which a light source is on one end (left endin the figure), in which the profile curve 401 is divided into 7segments, and the slope α on the side of the light source and the slopeβ on the opposite side are separated by a dotted line. Regarding therough surface patterns contained in each segment of this profile curve,the average of absolute values of slopes α on the side of the lightsource is made to increase as it approaches closer to the light source,or as it moves from segment 7 to segment 1, whereas the average ofabsolute values of slopes β on the opposite side of the light source ismade to decrease as it moves from segment 7 to segment 1. By thuschanging the slope in accordance with the distance from the light sourceand depending on whether the slope is towards the light source or not,the ratio of the emergent light oriented to the front direction can beincreased even near the light source, thereby increasing the uniformityof luminance.

FIG. 12 shows the case in which a light source is on both ends, whereinthe profile curve 401 is also divided into 7 segments, and the slopes αon the side of the left light source and the slopes β on the right sideof the light source are separated by a dotted line. In this case, theaverage of absolute values of slopes α on the left light source sidecontained in each segment is made to increase as it approaches closer tothe left light source, namely it moves from segment 7 to segment 1,whereas the average of absolute values of slopes β on the right lightsource side is made to increase as it approaches closer the right lightsource, namely it moves from segment 1 to segment 7. Also in this case,by correcting the tendency that the luminance at the emergent angleleaning greatly from the front is increased as approaching the lightsource, the front luminance can be improved and be made uniform.

Conditions to be satisfied by the rough surface pattern of the lightcontrol film of this invention for obtaining optimal luminance areexplained above relative to the light source. Also in this case,regarding substantially all cross sections, each profile curve needs tosatisfy either of the aforementioned Conditions 1-4.

The geometry or configuration of the protrusion of the light controlfilm of this invention is not limited as far as the profile curve of therough surface patterns satisfies the aforementioned conditions, but theprotrusions and recesses are preferably arranged randomly. By thisrandom arrangement, the aforementioned conditions can be satisfied moreeasily for substantially all cross sections and the generation ofinterference patterns is prevented. Each protrusion and recess can beshaped same or differently, and can be placed one upon another. Or, apart or all protrusions and recesses can be arranged to be piled up. Theheight of protrusion and the depth of recess is preferably about 3-100μm and the protrusions or recesses are arranged preferably in a densityof 10-200,000 protrusions or recesses/mm². Typical rough surfacepatterns of a light control film which satisfies aforementionedconditions are shown in FIG. 13.

Concrete configurations for producing a light control film havingaforementioned rough surface patterns will be explained below.

As materials for producing a substrate 11 and a rough surface patternlayer 12 of the light control film of this invention, any materialgenerally used for optical films can be used. Substrate 11 can beproduced with any material having a good light transmittance, includingbut not limited to polyethylene terephthalate, polybutyleneterephthalate, polyethylene naphthalate, polycarbonates, polyethylenes,polypropylenes, polystyrenes, triacetyl cellulose, acrylic, polyvinylchloride and other plastic films.

Material for producing a rough surface patterned layer 12 can also beany material having a good light transmittance, including but notlimited to glass and polymer resin. Examples of such glass includeoxidized glass, such as silicate glass, phosphate glass and borateglass. Examples of such polymer resin include thermoplastic resin,thermosetting resin and ionizing radiation setting resin, such aspolyester resin, acrylic resin, acrylic urethane resin, polyesteracrylate resin, polyurethane acrylate resin, epoxy acrylate resin,urethane resin, epoxy resin, polycarbonate resin, cellulose resin,acetal resin, vinyl resin, polyethylene resin, polystyrene resin,polypropylene resin, polyamide resin, polyimide resin, melamine resin,phenol resin, silicone resin and fluorine resin.

Among these materials, polymer resin, particularly that having arefraction index (JIS-K7142:1996) of 1.3-1.7, is preferably used fromthe standpoint of good processibility and handlability. Even if amaterial whose refraction index n is not within the aforementioned rangeis used as a material for forming a rough surface pattern, goodluminance can be attained if the rough surface pattern thus formedsatisfies condition 1 or condition 3. However, high luminance can beobtained obviously by using the material with a refraction index withinsuch range. In particular, the front luminance can be further improvedby making the rough surface pattern satisfy condition 2 or condition 4according to the refraction index n of the material.

The rough surface patterned layer 12 may contain light diffusion agents,such as organic beads and inorganic pigments as an ordinary lightdiffusion sheet, but the light diffusion agents are not indispensable.In the light control film of this invention, the rough surface patternitself can give some extent of light diffusion effects, without addingsuch light diffusion agent. Accordingly, any damage of other materialcaused by the light diffusion agent or the generation of waste ofexfoliated light diffusion agent will not occur.

The rough surface patterned layer 12 can be formed by using, forexample, (1) emboss roll methods (2) etching processing or (3) molding.In a sense that a light control film with certain rough surface patternscan be produced with high reproducibility, the use of the molding methodis preferable. Concretely, the light control film having such roughsurface patterns can be produced by producing a mold having a patternsymmetrical to the rough surface pattern, pouring material for producingrough surface patterns, including polymer resin into said mold andtaking out the material after setting. When a substrate is used, therough surface pattern can be produced by pouring polymer resin etc.,into a mold, placing a transparent substrate on it, setting the polymerresin, and taking it out together with the transparent substrate fromthe mold.

The methods for producing a pattern symmetrical to the rough surfacepattern on a mold include but not limited to the following methods: Arough surface pattern in which one of the protrusions satisfies Formula(1) is formed on a flat surface with a density of several thousands/mm²by using a laser micro-processing technology. Then, by using this as amale mold, a female mold to be used for molding is produced. Severaldifferent blocks, which have a different slope of the rough surfacepattern, are produced. Then a male mold for a light control film isproduced by placing these blocks in certain arrangement, and a femalemold is produced using this male mold. Alternatively, after producing aresin plate having unevenness by setting the resin in which particles ofa certain size are dispersed, such rough surface patterned surface ismeasured by using a surface profiler and a resin plate which satisfiesthe aforementioned conditions is chosen. The plate thus chosen is usedas a male mold to produce a female mold for molding.

The surface of a light control film, opposite to the rough surfacepatterned surface can be flat or smooth, but it can be subjected tomicro-matting treatment to prevent the generation of the Newton ringswhen contacting with a light guiding plate or resin plate, and/or to theanti-reflection treatment to improve light transmittance.

Further, in order to obtain a good front luminance, the Haze, one of theoptical characteristics, should be 60% or higher, or preferably 70% orhigher, wherein Haze is a value of Haze based on JIS-K7136:2000, and canbe obtained from the formula, Haze (%)=[(τ₄/τ₂)−τ₃(τ₂/τ₁)]×100 (τ₁:bundle of incident light, τ₂: total bundle transmitting a specimen, τ₃bundle diffused in a device, τ₄: bundle diffused in a device andspecimen).

There is no limitation on thickness of a light control film as a whole,but the film is approximately 20-300 μm thick in general.

The light control film of the invention as explained above is usedmainly as a component of a back light composing a liquid crystaldisplay, illuminated sign and others.

A backlight of this invention will be explained below. The backlight ofthis invention comprises at least a light control film and a lightsource. The aforementioned light control film is used as a light controlfilm. No limitation is applied to the direction of the light controlfilm in a backlight, but the rough surface patterned side is usedpreferably as the light emergent side. The backlight preferably employsa configuration, as called edge-light or direct type.

An edge-light backlight comprises a light guiding plate, a light sourcelocated on at least one end of the light guiding plate, a light controlfilm located on the light emergent side of the light guiding plate etc.,where the light control film is preferably used as the rough surfacepatterned surface represents a light emergent surface.

A light guiding plate comprises an almost flat plate which is molded sothat at least one side represents a light incident surface and the othersurface orthogonally crossing said surface represents a light emergingsurface, and is made of matrix resin selected from highly transparentresins mainly including polymethylmetacrylate. Resin particles with adifferent refraction index from that of the matrix resin may be added,in line with the purpose of use. Every surface of the light guidingplate needs not to be uniformly flat, but may be complicatedly shaped ormay have diffusion prints such as a dot pattern.

As a light source, which should be located on at least one end of thelight guiding plate, a cold cathode ray tube is mainly used. The shapeof the light source maybe linear, L-shaped, etc.

An edge-light backlight is equipped with, in addition to theaforementioned light control film, a light guiding plate and a lightsource, a reflective plate, a polarizing film, an electromagnetic shieldfilm, etc., in line with the purpose of use.

An embodiment of the edge-light backlight of this invention is shown inFIG. 14. This backlight 140 has a configuration, in which a light source142 is placed on both ends of the light guiding plate 141, on which alight control film 143 is placed as the rough surface patterned surfacerepresents the outer side. The light source 142 is covered by a lightsource reflector 144, except the part opposing to the light guidingplate 141, to make the light from the light source enters effectivelyinto the light guiding plate 141. Further, a reflective plate 146 storedin a chassis 145 is located under the light guiding plate 141, to returnthe light emerging to the other side of the emergent side of the lightguiding plate 141, thereby increasing the emergent light from theemergent surface of the light guiding plate 141.

The direct backlight comprises a light control film and an lightdiffusion material and a light source located on the surface opposite tothe light emergent surface of the light control film, in which the lightcontrol film is used preferably as a rough surface patterned surfacerepresents a light emergent surface.

As the light diffusion material, which is used for the purpose ofeliminating the pattern of the light source, in addition to atransparent film (lighting curtain) having a dot pattern in a positioncorresponding to the light source, so called light diffusion film havingan uneven light diffusion layer on the transparent substrate can be usedalone or in combination with others, as it is deemed appropriate.

A cold cathode ray tube is mainly used as the light source. The shape ofthe light source may be linear, L-shaped, etc. A direct backlight may beequipped with, in addition to aforementioned light control film, a lightguiding plate and a light source, a reflective plate, a polarizing film,an electromagnetic shield film, etc., in line with the purpose of use.

An embodiment of the direct backlight of this invention is shown in FIG.15. The backlight 150 has a structure, as illustrated in the figure, inwhich multiple units of light source 152 are placed on the light guidingplate 156 stored in the chassis 155, and the light control film 153 islaminated on the light source via the light diffusion material 157.

By using a light control film with a particular rough surface pattern,as a light control film for controlling the direction of a lightemerging from a light source or a light guiding plate, the backlight ofthis invention can have a dramatically improved front luminance ascompared with that of conventional backlights, without generating glareand/or interference patterns often observed when a prism sheet is used.

EXAMPLES

Examples of this invention will be explained in detail.

Examples 1-5

Five different molds (1)-(5) on which a certain rough surface patternwas formed by using a laser micro-processing technology were produced.Then, the light control films (1)-(5) of 23 cm (in directionperpendicular to a light source)×31 cm (in direction parallel to a lightsource) were produced by pouring silicon resin with a refraction indexof 1.40 into a mold (1) and ultraviolet setting resin with a refractionindex of 1.50 into molds (2)-(5), setting the poured resin and takingthem out from the molds.

Then, the profile of the rough surface patterned surface (light emergentsurface) of the light control films (1)-(5) was measured according toJIS B 0651 by using a surface profiler (SAS-2010 SAU-II: Meishin KokiCo. Ltd.). The shape of a stylus used in this surface profiler wasconical with a globe on a tip, where a tip radius is 2 μm and a taperangle is 60 degree. Measurement interval was 1.0 μm. The measurement wasconducted on 5 positions on each light control film, and the average ofthe absolute values of slope to the light incident surface wascalculated by using profile curves in different directions. These 5measurement points on the film are points A-E as shown in FIG. 9, i.e.,5 points for dividing each of 2 virtual diagonal lines on the opticalfilm into 4 parts (excluding the starting and the end points of thediagonal line). Further, the measurement was conducted at every 15degree by rotating the profile curve anti-clockwise from the starting(zero degree) point—parallel to the light sources 91 and 92, tillreturning to the starting or parallel to the light source. (However, themeasurement at 180 degrees was excluded because it is the same with themeasurement at 0 degree). Results of the measurements for the opticalfilms (1)-(5) are shown in Tables 1-5 (unit is degree).

TABLE 1 A B C D E  0° 35.5 34.8 39.9 35.2 35.2  15° 39.9 39.6 40.1 39.839.9  30° 44.2 44.6 44.5 44.4 44.1  45° 47.5 47.5 47.5 47.4 47.6  60°49.8 49.6 49.4 49.4 49.8  75° 50.4 50.6 50.4 50.3 50.3  90° 51.4 51.451.1 50.9 51.1 105° 50.3 50.5 50.8 50.6 50.3 120° 49.2 49.8 49.7 50.049.4 135° 47.2 47.3 47.6 47.7 47.4 150° 44.4 43.9 44.6 44.4 44.6 165°39.7 39.8 39.8 39.9 39.8

TABLE 2 A B C D E  0° 32.4 31.7 36.4 32.1 32.2  15° 36.5 36.3 36.8 36.536.5  30° 40.7 41.2 41.1 41.0 40.6  45° 44.2 44.2 44.1 44.1 44.3  60°46.5 46.3 46.1 46.1 46.6  75° 47.2 47.4 47.1 47.0 47.1  90° 48.1 48.247.8 47.6 47.8 105° 47.1 47.2 47.6 47.3 47.1 120° 45.9 46.5 46.5 46.746.1 135° 43.8 44.0 44.2 44.4 44.0 150° 41.0 40.4 41.1 41.0 41.3 165°36.3 36.4 36.4 36.6 36.5

TABLE 3 A B C D E  0° 33.5 33.2 33.1 32.6 33.0  15° 38.4 38.1 37.9 37.838.2  30° 44.1 44.0 43.9 44.0 44.1  45° 47.9 47.8 47.9 47.9 48.0  60°50.4 50.7 50.5 50.4 50.5  75° 51.7 52.0 51.9 51.8 51.7  90° 52.5 52.852.7 52.4 52.5 105° 51.7 52.0 51.9 51.8 51.6 120° 50.4 50.6 50.7 50.450.4 135° 47.9 48.2 48.0 47.9 47.9 150° 44.2 44.4 44.2 43.9 43.9 165°38.4 38.3 38.1 37.8 37.9

TABLE 4 A B C D E  0° 38.6 38.6 38.6 38.6 38.5  15° 38.1 38.1 38.2 38.238.2  30° 38.3 38.4 38.5 38.7 38.9  45° 38.9 38.6 38.4 38.1 37.8  60°37.6 37.5 37.7 37.7 38.1  75° 38.6 39.0 39.4 39.4 39.0  90° 38.5 37.937.3 37.1 37.3 105° 37.8 38.2 38.8 39.0 39.0 120° 38.9 38.6 38.2 37.737.4 135° 37.5 37.5 37.9 38.3 38.6 150° 37.7 38.3 37.8 37.8 38.8 165°38.2 38.6 38.1 39.0 38.6

TABLE 5 A

B

C

D

E

 0° 25.5 25.5 25.5 25.5 25.5  15° 25.2 25.3 25.3 25.3 25.4  30° 25.425.4 25.4 25.5 25.5  45° 25.6 25.4 25.4 25.3 25.2  60° 25.2 25.1 25.325.2 25.3  75° 25.5 25.6 25.8 25.8 25.7  90° 25.6 25.3 24.9 24.9 25.0105° 25.4 25.5 25.7 25.7 25.7 120° 25.6 25.6 25.4 25.2 25.1 135° 25.125.2 25.3 25.5 25.7 150° 25.6 25.2 25.3 25.3 25.4 165° 25.6 25.5 25.625.7 25.4

As the data in Tables 1-5 indicates, the light control films of Exampleshave the average of absolute values of slope of a profile curve of 20degrees or higher and 75 degrees or lower in all directions at allmeasuring points. Further, as the data in Tables 1-3 clearly shows, theaverage of absolute values of slope in the light control films (1)-(3)increases as the direction of a profile curve moves from parallel (0 and180 degree) to perpendicular (90 degree) to the light source.

Then, the profile curve in direction perpendicular (direction y in FIG.9) to the light source (cold cathode ray tube) of the backlight atpoints A, C and E of the light control films (1)-(5) were divided into 7segments, and the average of absolute values of slope of the incliningsurface on the light source side and on the opposite side of the lightsource of each profile curve was calculated by each divided interval.Results obtained for the light control films (1)-(5) are shown in Tables6-10 (Unit: degree). The results of measurement were divided into twodepending on whether the standard light source is the light source 91 orthe light source 92, and divided segments were defined as segment 1 tosegment 7 as it approaches from the light source 91 to the light source92.

TABLE 6 point A point C point E Light Light Light Source Opposite SourceOpposite Source Opposite Side Side Side Side Side Side From Light Source91 Segment1 57.1 42.7 57.0 42.8 57.4 42.7 Segment2 56.0 48.5 56.0 48.756.2 48.6 Segment3 54.1 52.4 54.4 52.8 54.4 52.7 Segment4 53.3 53.3 53.753.6 53.4 53.5 Segment5 52.6 54.4 52.5 54.1 52.2 54.0 Segment6 48.6 56.048.4 55.8 48.2 55.3 Segment7 42.8 57.5 42.5 56.9 42.4 56.5 From LightSource 92 Segment1 42.7 57.1 42.8 57.0 42.7 57.4 Segment2 48.5 56.0 48.756.0 48.6 56.2 Segment3 52.4 54.1 52.8 54.4 52.7 54.4 Segment4 53.3 53.353.6 53.7 53.5 53.4 Segment5 54.4 52.6 54.1 52.5 54.0 52.2 Segment6 56.048.6 55.8 48.4 55.3 48.2 Segment7 57.5 42.8 56.9 42.5 56.5 42.4

TABLE 7 point A point C point E Light Light Light Source Opposite SourceOpposite Source Opposite Side Side Side Side Side Side From Light Source91 Segment1 54.1 39.3 54.1 39.3 54.4 39.3 Segment2 52.9 44.9 52.9 45.153.1 45.0 Segment3 51.4 48.6 51.4 49.1 51.7 48.9 Segment4 50.5 50.4 50.950.7 50.7 50.7 Segment5 48.8 51.6 48.7 51.4 48.4 51.2 Segment6 44.9 53.144.8 52.8 44.5 52.3 Segment7 39.5 54.4 39.1 54.0 38.9 53.6 From LightSource 92 Segment1 39.3 54.1 39.3 54.1 39.3 54.4 Segment2 44.9 52.9 45.152.9 45.0 53.1 Segment3 48.6 51.4 49.1 51.4 48.9 51.7 Segment4 50.4 50.550.7 50.9 50.7 50.7 Segment5 51.6 48.8 51.4 48.7 51.2 48.4 Segment6 53.144.9 52.8 44.8 52.3 44.5 Segment7 54.4 39.5 54.0 39.1 53.6 38.9

TABLE 8 point A point C point E Light Light Light Source Opposite SourceOpposite Source Opposite Side Side Side Side Side Side From Light Source91 Segment1 52.5 52.6 52.4 52.4 52.6 52.7 Segment2 52.8 52.8 52.4 52.352.4 52.4 Segment3 52.9 52.6 52.6 52.4 52.4 52.4 Segment4 52.5 52.4 52.652.3 52.0 52.2 Segment5 52.5 52.5 52.6 52.3 52.1 52.2 Segment6 52.3 52.152.7 52.7 52.2 52.0 Segment7 52.1 52.2 52.7 53.1 52.1 52.3 From LightSource 92 Segment1 52.6 52.5 52.4 52.4 52.7 52.6 Segment2 52.8 52.8 52.352.4 52.4 52.4 Segment3 52.6 52.9 52.4 52.6 52.4 52.4 Segment4 52.4 52.552.3 52.6 52.2 52.0 Segment5 52.5 52.5 52.3 52.6 52.2 52.1 Segment6 52.152.3 52.7 52.7 52.0 52.2 Segment7 52.2 52.1 53.1 52.7 52.3 52.1

TABLE 9 point A point C point E Light Light Light Source Opposite SourceOpposite Source Opposite Side Side Side Side Side Side From Light Source91 Segment1 40.4 40.4 40.6 40.5 40.9 40.6 Segment2 40.5 40.5 40.5 40.740.3 40.5 Segment3 41.0 40.8 40.6 40.7 40.1 40.4 Segment4 41.0 41.0 40.740.5 40.0 40.1 Segment5 40.7 40.7 40.6 40.5 40.0 40.0 Segment6 40.1 40.240.7 40.6 40.0 39.9 Segment7 40.2 40.3 40.9 41.1 40.0 40.3 From LightSource 92 Segment1 40.4 40.4 40.5 40.6 40.6 40.9 Segment2 40.5 40.5 40.740.5 40.5 40.3 Segment3 40.8 41.0 40.7 40.6 40.4 40.1 Segment4 41.0 41.040.5 40.7 40.1 40.0 Segment5 40.7 40.7 40.5 40.6 40.0 40.0 Segment6 40.240.1 40.6 40.7 39.9 40.0 Segment7 40.3 40.2 41.1 40.9 40.3 40.0

TABLE 10 point A point C point E Light Light Light Source OppositeSource Opposite Source Opposite Side Side Side Side Side Side From LightSource 91 Segment1 25.5 25.5 25.3 25.3 25.5 25.6 Segment2 25.5 25.5 25.325.3 25.7 25.4 Segment3 25.5 25.5 25.4 25.4 25.4 25.3 Segment4 25.5 25.625.4 25.4 25.4 25.4 Segment5 25.5 25.5 25.4 25.3 25.3 25.4 Segment6 25.225.3 25.4 25.4 25.2 25.3 Segment7 25.2 25.3 25.5 25.4 25.2 25.2 FromLight Source 92 Segment1 25.5 25.5 25.3 25.3 25.6 25.5 Segment2 25.525.5 25.3 25.3 25.4 25.7 Segment3 25.5 25.5 25.4 25.4 25.3 25.4 Segment425.6 25.5 25.4 25.4 25.4 25.4 Segment5 25.5 25.5 25.3 25.4 25.4 25.3Segment6 25.3 25.2 25.4 25.4 25.3 25.2 Segment7 25.3 25.2 25.4 25.5 25.225.2

As clearly shown in Table 6 and Table 7, in the light control films (1)and (2), when the light source 91 (FIG. 9) is standard, the average ofabsolute values of slope of the inclining plane on the side of lightsource 91 increases as it approaches from segment 7 to segment 1. Whenthe light source 92 is a standard (base point), the average of absolutevalues of slope of the inclining plane on the side of light source 92increases as it approaches from segment 1 towards segment 7.

Haze values measured for each light control film in Examples 1-5 using ahaze meter (HGM-2K: Suga Shikenki) were 91.3, 90.8, 90.1, 85.3 and 82.1for light control film (1), (2), (3), (4) and (5), respectively. All ofthem satisfied optical characteristics required for obtaining good frontluminance.

Then, each of the light control films (1)-(5) was incorporated into a15-inch edge-light backlight (a cold cathode ray tube on both upper andlower position) to measure the front luminance. Specifically, the lightcontrol films (1)-(5) were placed on a light guiding plate as the roughsurface patterned surface of the film becomes a light emergent surface,and the luminance at each emergent angle in direction parallel(direction x in FIG. 9) and perpendicular (direction-y in FIG. 9) to thelight source (cold cathode ray tube) was measured at points A-E on thebacklight (1 inch=2.54 cm). Results obtained for the light control films(1)-(5) are shown in Tables 11-15, in this order (Unit: cd/m²)

TABLE 11 A B C D E Horizontal L45° 1070 1080 1170 1070 1060 Direction xL30° 1310 1310 1410 1310 1320 0° 2750 2750 2960 2760 2770 R30° 1320 13301430 1310 1300 R45° 1080 1060 1170 1050 1070 Vertical U45° 1150 11401260 1380 1390 Direction y U30° 1280 1270 1420 1620 1620 0° 2750 27502960 2760 2770 D30° 1610 1610 1410 1270 1270 D45° 1370 1380 1250 11501140

TABLE 12 A B C D E Horizontal L45° 1040 1060 1170 1050 1050 Direction xL30° 1290 1310 1400 1310 1300 0° 2720 2720 2930 2720 2700 R30° 1280 12901400 1290 1290 R45° 1050 1050 1180 1050 1050 Vertical U45° 1130 11401230 1390 1370 Direction y U30° 1260 1250 1420 1630 1630 0° 2720 27202930 2720 2700 D30° 1630 1630 1420 1240 1250 D45° 1390 1370 1240 11501130

TABLE 13 A B C D E Horizontal L45° 1050 1040 1160 1040 1050 Direction xL30° 1270 1280 1360 1260 1270 0° 2630 2630 2900 2620 2620 R30° 1280 12701380 1280 1260 R45° 1040 1050 1150 1040 1030 Vertical U45° 1110 11201220 1390 1370 Direction y U30° 1210 1220 1410 1650 1660 0° 2630 26302900 2620 2620 D30° 1660 1650 1420 1220 1220 D45° 1360 1370 1220 11101110

TABLE 14 A B C D E Horizontal L45° 1000 978 1490 992 987 Direction xL30° 1900 1880 2000 1900 1870 0° 2090 2100 2380 2100 2090 R30° 1890 18902010 1880 1900 R45° 992 1010 1480 993 1010 Vertical U45° 1000 996 11701460 1460 Direction y U30° 1790 1810 2120 2570 2560 0° 2090 2100 23802100 2090 D30° 2570 2580 2120 1820 1810 D45° 1460 1450 1170 978 996

TABLE 15 A B C D E Horizontal L45° 996 975 1090 993 978 Direction x L30°1670 1640 1850 1670 1650 0° 1810 1820 2030 1800 1820 R30° 1650 1660 18401630 1670 R45° 987 1000 1090 974 1000 Vertical U45° 987 996 1200 17901810 Direction y U30° 1550 1560 2100 2770 2780 0° 1810 1820 2030 18001820 D30° 2780 2770 2090 1560 1560 D45° 1790 1800 1210 1000 995

These results indicate that a good front luminance can be obtained byincorporating only one sheet of the light control film of Examples.Particularly, in the light control films (1)-(3), since the average ofabsolute values of slope of a profile curve increases as the directionof the profile curve moves from parallel (0 and 180 degree) toperpendicular (90 degree) to the light source, the backlightincorporating such light control film could efficiently orient the lightleaning greatly from the front in direction perpendicular to the lightsource towards the direction to the front, thus attaining a good frontluminance. In comparison of figures in Tables 11-13 with that in Tables14 and 15, it is shown that, in the former, the front luminance ishigher, and that the luminance at upper and lower 30 degrees and 40degrees in vertical direction are considerably small relative to theluminance in front direction, thus suggesting that the light iseffectively oriented towards the front.

In the light control films (1) and (2) in which the average of absolutevalues of slope of the inclining surface on the side of the light source91 increases as it approaches closer to the light source, the lightgreatly leaning from the front (0 degree) in direction perpendicular tothe light source can be effectively oriented to the front direction evenat the points A, B, D and E, which are closer to the light source ratherthan to the center of the film (point C), thus attaining a good frontluminance. In comparison of values in Tables 11 and 12 with those inTables 13-15, difference in the front luminance between point C andpoints A, B, D and E is smaller in the Tables 11 and 12 and, with regardto vertical directions at points A, B, D and E, difference in luminancebetween upper 30 degree and lower 30 degree and between upper 45 degreeand lower 45 degree are smaller, and are sufficiently smaller than theluminance in the front direction. It can be understood from this thatthe light is efficiently oriented to the front by reducing influence ofpositional change (polarization) of emergent light.

Examples 6-8

Three different molds (6)-(8) on which a certain rough surface patternis formed by laser micro-processing technology were produced. Lightcontrol films (6)-(8) of 23 cm×31 cm were produced by pouringultraviolet setting resin with a refraction index of 1.50 into molds (6)and (7) and silicon resin with refraction index of 1.40 into molds (8),setting the poured resin and taking them out from the molds.

Then, the profiles of the surface (light emergent surface) with therough surface pattern of the light control films (6)-(8) were measuredby using a laser microscope (VK-8500: KEYENCE) with an objective lenswith magnification [×50]. Measurement interval was 0.29 μm. A profilecurve was obtained by applying a low pass filter with a cutoff value of2.5 μm to the measured profile curve, and the average of absolute valuesof slope (θ_(ave)) to the light incident surface of this profile curvewas calculated. In the same manner as in Examples of 1-5 the measurementwas conducted at 5 positions on each light control film to calculate theaverage of absolute values of slope to the light incident surface foreach profile curve of different direction. Further, by measuring thelength (L2) of each profile curve and calculating its ratio to thelength (L1) of the bottom of the section (Lr=L2/L1), the product orquotient between the average of absolute values of slope (θ_(ave)) andthe length ratio (Lr) were obtained.

Measurements obtained at 5 points A-E of each light control film (6)-(8)are shown in Tables 16-18 in order. Further, the averages of allmeasurements (θ_(ave), Lr, θ_(ave)/Lr, θ_(ave)×Lr) at five points A-Eare shown in Table 19.

Haze values obtained for each light control film in examples 6-8 using ahaze meter (HGM-2K: Suga Shikenki) are also shown in Table 19.

TABLE 16 A B Average Average of Slope L2/L1 ÷ × of Slope L2/L1 ÷ ×  0°35.6 1.33 26.7 47.5 35.1 1.33 26.5 46.5  15° 35.5 1.33 26.6 47.3 35.01.32 26.5 46.4  30° 35.4 1.33 26.6 47.1 35.2 1.33 26.5 46.6  45° 35.41.33 26.6 47.0 35.5 1.33 26.7 47.3  60° 35.4 1.33 26.6 47.0 35.6 1.3326.7 47.5  75° 35.3 1.33 26.5 46.9 35.8 1.34 26.8 47.9  90° 35.4 1.3326.6 47.1 36.1 1.34 26.9 48.5 105° 35.4 1.33 26.6 47.1 36.1 1.34 26.948.6 120° 35.3 1.33 26.6 46.8 36.1 1.34 26.9 48.6 135° 35.1 1.33 26.546.6 35.9 1.34 26.8 48.0 150° 35.1 1.33 26.5 46.5 35.7 1.33 26.7 47.6165° 35.1 1.33 26.5 46.5 35.4 1.33 26.7 47.1 C D Average Average ofSlope L2/L1 ÷ × of Slope L2/L1 ÷ ×  0° 35.2 1.33 26.5 46.6 35.2 1.3226.6 46.6  15° 34.8 1.32 26.4 46.0 35.2 1.32 26.6 46.6  30° 34.9 1.3226.4 46.1 35.3 1.33 26.6 46.8  45° 34.9 1.32 26.4 46.3 35.4 1.33 26.647.1  60° 35.0 1.33 26.4 46.5 35.5 1.33 26.6 47.4  75° 35.3 1.33 26.547.0 35.7 1.34 26.7 47.8  90° 35.6 1.33 26.7 47.4 35.8 1.34 26.7 47.9105° 35.7 1.33 26.7 47.6 35.6 1.34 26.7 47.5 120° 35.7 1.33 26.7 47.635.3 1.33 26.6 46.9 135° 35.6 1.33 26.7 47.5 35.0 1.32 26.5 46.3 150°35.4 1.33 26.6 47.1 34.7 1.32 26.3 45.7 165° 35.3 1.33 26.6 46.8 34.71.32 26.3 45.7 E Average of Slope L2/L1 ÷ ×  0° 34.5 1.32 26.2 45.5  15°34.7 1.32 26.3 45.9  30° 35.0 1.33 26.4 46.5  45° 35.3 1.33 26.6 47.0 60° 35.7 1.33 26.8 47.7  75° 36.0 1.34 26.9 48.2  90° 36.1 1.34 26.948.3 105° 36.1 1.34 26.9 48.3 120° 36.0 1.34 26.9 48.2 135° 36.0 1.3426.9 48.3 150° 35.9 1.34 26.8 48.1 165° 35.8 1.34 26.8 47.8

TABLE 17 A B Average Average of Slope L2/L1 ÷ × of Slope L2/L1 ÷ ×  0°27.7 1.18 23.5 32.7 27.4 1.18 23.3 32.2  15° 27.6 1.18 23.5 32.6 27.31.17 23.3 32.1  30° 27.6 1.18 23.4 32.5 27.4 1.18 23.3 32.2  45° 27.61.18 23.4 32.5 27.7 1.18 23.5 32.6  60° 27.6 1.18 23.4 32.5 27.7 1.1823.5 32.7  75° 27.5 1.18 23.4 32.4 27.9 1.18 23.6 32.9  90° 27.6 1.1823.4 32.5 28.1 1.18 23.8 33.3 105° 27.7 1.18 23.5 32.6 28.2 1.18 23.833.4 120° 27.5 1.18 23.4 32.4 28.2 1.18 23.8 33.4 135° 27.4 1.18 23.332.2 28.0 1.18 23.7 33.0 150° 27.4 1.18 23.3 32.2 27.8 1.18 23.6 32.8165° 27.4 1.18 23.3 32.2 27.6 1.18 23.5 32.5 C D Average Average ofSlope L2/L1 ÷ × of Slope L2/L1 ÷ ×  0° 27.4 1.17 23.3 32.2 27.4 1.1723.3 32.2  15° 27.1 1.17 23.1 31.8 27.4 1.17 23.3 32.2  30° 27.2 1.1723.2 31.9 27.5 1.18 23.4 32.3  45° 27.2 1.17 23.2 32.0 27.6 1.18 23.432.5  60° 27.3 1.18 23.2 32.1 27.7 1.18 23.5 32.7  75° 27.5 1.18 23.432.4 27.9 1.18 23.6 33.0  90° 27.7 1.18 23.5 32.7 27.9 1.18 23.6 33.0105° 27.8 1.18 23.6 32.8 27.8 1.18 23.5 32.8 120° 27.8 1.18 23.6 32.827.5 1.18 23.4 32.4 135° 27.8 1.18 23.5 32.8 27.3 1.17 23.2 32.0 150°27.6 1.18 23.4 32.5 27.0 1.17 23.1 31.6 165° 27.5 1.18 23.4 32.3 27.01.17 23.0 31.6 E Average of Slope L2/L1 ÷ ×  0° 26.9 1.17 23.0 31.5  15°27.1 1.17 23.1 31.8  30° 27.3 1.18 23.3 32.1  45° 27.6 1.18 23.4 32.5 60° 27.9 1.18 23.6 32.9  75° 28.1 1.18 23.8 33.2  90° 28.1 1.18 23.833.3 105° 28.1 1.18 23.8 33.2 120° 28.1 1.18 23.7 33.2 135° 28.1 1.1823.7 33.2 150° 28.0 1.18 23.7 33.1 165° 27.9 1.18 23.6 32.9

TABLE 18 A B Average Average of Slope L2/L1 ÷ × of Slope L2/L1 ÷ ×  0°25.0 1.22 20.4 30.6 24.8 1.22 20.3 30.3  15° 24.6 1.22 20.2 30.1 24.81.22 20.3 30.4  30° 24.5 1.22 20.1 30.0 24.8 1.22 20.3 30.4  45° 24.51.22 20.1 30.0 24.9 1.22 20.3 30.5  60° 24.5 1.22 20.0 29.9 24.8 1.2220.3 30.4  75° 24.5 1.23 20.0 30.0 24.5 1.22 20.1 30.0  90° 24.6 1.2320.0 30.2 25.1 1.22 20.5 30.7 105° 24.5 1.23 20.0 30.0 24.6 1.22 20.130.1 120° 24.6 1.23 20.1 30.2 24.5 1.22 20.1 30.0 135° 24.7 1.23 20.130.3 24.7 1.22 20.2 30.2 150° 24.9 1.23 20.3 30.5 24.5 1.22 20.0 29.9165° 24.8 1.23 20.2 30.4 24.5 1.22 20.0 29.9 C D Average Average ofSlope L2/L1 ÷ × of Slope L2/L1 ÷ ×  0° 24.7 1.22 20.2 30.1 25.0 1.2320.3 30.8  15° 24.7 1.22 20.3 30.2 25.0 1.23 20.4 30.7  30° 25.1 1.2220.5 30.7 24.7 1.22 20.2 30.3  45° 25.3 1.23 20.6 31.0 25.1 1.22 20.630.6  60° 25.4 1.23 20.7 31.2 24.7 1.22 20.1 30.2  75° 25.3 1.23 20.631.1 24.9 1.22 20.3 30.5  90° 25.1 1.23 20.4 30.8 24.8 1.22 20.3 30.4105° 24.9 1.23 20.2 30.6 24.5 1.22 20.1 30.0 120° 25.1 1.23 20.3 30.924.5 1.22 20.1 30.0 135° 25.1 1.23 20.3 31.0 24.7 1.22 20.3 30.1 150°25.2 1.23 20.4 31.1 24.8 1.22 20.3 30.3 165° 25.2 1.23 20.4 31.0 24.61.23 20.1 30.1 E Average of Slope L2/L1 ÷ ×  0° 25.1 1.23 20.4 30.8  15°25.3 1.23 20.5 31.1  30° 25.3 1.23 20.5 31.1  45° 25.2 1.23 20.4 31.1 60° 25.3 1.23 20.5 31.3  75° 25.2 1.23 20.5 31.1  90° 25.3 1.23 20.531.1 105° 25.3 1.23 20.5 31.1 120° 25.4 1.23 20.6 31.3 135° 25.4 1.2320.6 31.2 150° 25.4 1.23 20.6 31.2 165° 25.2 1.23 20.5 30.8

TABLE 19 Haze (%) av. slope Lratio θ ave/Lr θ ave * Lr Example6 93.435.4 1.33 26.6 47.1 Example7 90.2 27.6 1.18 23.4 32.5 Example8 83.2 24.91.23 20.3 30.5

As shown in Tables 16-18, in the light control films (6)-(8), varianceof both average of absolute values of slope and length ratio were smallat all measurement points and in all directions, thus indicating thepresence of uniform unevenness characteristics on the as a whole. Hazeof 80% or higher was obtained in all Examples.

Then, the light control films (6)-(8) were incorporated into anedge-light backlight as shown in FIG. 14, and a luminance distribution(emergent angle distribution) at the horizontal direction of ±45° andvertical direction of ±45° was measured. Results obtained in themeasurements at 5 positions A-E, corresponding to the surface geometrymeasurement points, are shown in Tables 20-22. The unit of the figures(luminance) in the tables is cd/m². Distributions of luminance in thehorizontal and vertical directions at the point C of the backlightaccording to embodiment 1 are shown in FIG. 16.

TABLE 20 A B C D E Horizontal L45° 977 960 1090 977 964 Direction x L30°1860 1840 2010 1850 1830 0° 2110 2130 2310 2130 2120 R30° 1840 1860 20201850 1870 R45° 960 979 1090 969 983 Vertical U45° 949 950 1140 1430 1420Direction y U30° 1740 1730 2080 2540 2530 0° 2110 2130 2310 2130 2120D30° 2530 2530 2060 1740 1750 D45° 1430 1430 1150 960 950

TABLE 21 A B C D E Horizontal L45° 1210 1210 1320 1190 1210 Direction xL30° 1620 1620 1830 1610 1620 0° 1840 1830 2120 1840 1840 R30° 1620 16001850 1610 1610 R45° 1220 1210 1330 1220 1200 Vertical U45° 1200 12101480 2380 2380 Direction y U30° 1700 1710 2180 2850 2870 0° 1840 18302120 1840 1840 D30° 2860 2860 2210 1710 1710 D45° 2380 2380 1460 12101210

TABLE 22 A B C D E Horizontal L45° 985 971 1070 970 961 Direction x L30°1650 1620 1830 1650 1630 0° 1790 1790 2010 1790 1780 R30° 1620 1640 18201630 1640 R45° 961 986 1080 959 972 Vertical U45° 988 975 1200 1780 1790Direction y U30° 1560 1550 2070 2760 2750 0° 1790 1790 2010 1790 1780D30° 2770 2750 2070 1540 1540 D45° 1790 1790 1200 977 979

As the results in FIG. 16 indicate, the light control film of Examplescould attain a high luminance within 40° and produced an emergent lightequal to or higher than that attained by a prism sheet in the frontdirection.

Comparative Examples 1-4

For commercially available prism sheets (Comparative example 1) andlight diffusion sheets (Comparative examples 2-4), the geometry of therough surface patterned surface (light emergent surface) was measured on5 points A-E on the film as in abovementioned examples 1-5, and theaverage of absolute values of slope (θ_(ave)) of the profile curve wasobtained. Results obtained in the measurements at 5 points A-E on eachlight control film in Comparative examples 1-4 are shown in this orderin Tables 23-26.

TABLE 23 A B Average Average of Slope L2/L1 ÷ × of Slope L2/L1 ÷ ×  0°0.2 1.00 0.2 0.2 0.4 1.00 0.4 0.4  15° 11.4 1.03 11.1 11.7 11.8 1.0311.5 12.2  30° 22.5 1.12 20.1 25.2 22.8 1.13 20.2 25.8  45° 32.0 1.2326.0 39.4 31.7 1.22 26.0 38.7  60° 38.9 1.32 29.5 51.3 38.6 1.32 29.251.0  75° 43.3 1.38 31.4 59.8 43.7 1.39 31.4 60.7  90° 44.7 1.41 31.763.0 45.0 1.41 31.9 63.5 105° 43.4 1.39 31.2 60.3 43.7 1.40 31.2 61.2120° 39.0 1.31 29.8 51.1 39.3 1.32 29.8 51.9 135° 32.1 1.22 26.3 39.231.5 1.21 26.0 38.1 150° 22.8 1.13 20.2 25.8 22.4 1.12 20.0 25.1 165°11.2 1.03 10.9 11.5 11.3 1.04 10.9 11.8 C D Average Average of SlopeL2/L1 ÷ × of Slope L2/L1 ÷ ×  0° 0.2 1.00 0.2 0.2 0.3 1.00 0.3 0.3  15°11.7 1.03 11.4 12.1 11.5 1.03 11.2 11.8  30° 22.2 1.12 19.8 24.9 22.31.13 19.7 25.2  45° 32.2 1.22 26.4 39.3 31.6 1.21 26.1 38.2  60° 39.21.33 29.5 52.1 38.6 1.32 29.2 51.0  75° 43.3 1.39 31.2 60.2 43.8 1.4031.3 61.3  90° 45.1 1.42 31.8 64.0 44.7 1.41 31.7 63.0 105° 43.5 1.3931.3 60.5 43.5 1.39 31.3 60.5 120° 38.7 1.32 29.3 51.1 38.5 1.31 29.450.4 135° 31.4 1.20 26.2 37.7 31.3 1.22 25.7 38.2 150° 22.9 1.13 20.325.9 22.1 1.11 19.9 24.5 165° 11.5 1.03 11.2 11.8 11.5 1.03 11.2 11.8 EAverage of Slope L2/L1 ÷ ×  0° 0.1 1.00 0.1 0.1  15° 12.0 1.02 11.8 12.2 30° 22.0 1.12 19.6 24.6  45° 31.6 1.22 25.9 38.6  60° 39.3 1.33 29.552.3  75° 43.3 1.39 31.2 60.2  90° 44.6 1.41 31.6 62.9 105° 43.7 1.3931.4 60.7 120° 39.2 1.32 29.7 51.7 135° 31.9 1.23 25.9 39.2 150° 22.21.12 19.8 24.9 165° 11.7 1.03 11.4 12.1

TABLE 24 A B Average Average of Slope L2/L1 ÷ × of Slope L2/L1 ÷ ×  0°13.3 1.05 12.7 13.9 12.7 1.04 12.2 13.2  15° 12.6 1.04 12.1 13.2 11.71.04 11.3 12.1  30° 13.2 1.04 12.6 13.7 11.7 1.04 11.3 12.2  45° 13.31.05 12.7 13.9 13.2 1.04 12.6 13.8  60° 12.8 1.05 12.2 13.4 12.8 1.0412.2 13.4  75° 12.9 1.04 12.4 13.4 12.5 1.04 12.0 13.0  90° 12.6 1.0412.1 13.1 13.2 1.05 12.6 13.8 105° 12.8 1.04 12.2 13.3 13.4 1.05 12.814.1 120° 12.2 1.04 11.7 12.7 12.0 1.04 11.6 12.5 135° 13.0 1.04 12.513.6 12.8 1.04 12.3 13.4 150° 12.4 1.04 12.0 12.9 13.1 1.05 12.5 13.7165° 13.0 1.04 12.5 13.6 12.4 1.04 11.9 12.9 C D Average Average ofSlope L2/L1 ÷ × of Slope L2/L1 ÷ ×  0° 12.6 1.04 12.1 13.1 12.2 1.0411.7 12.6  15° 13.2 1.05 12.6 13.8 12.7 1.04 12.2 13.3  30° 12.7 1.0412.2 13.2 13.3 1.05 12.7 13.9  45° 12.4 1.04 12.0 12.9 13.5 1.05 12.914.2  60° 13.3 1.04 12.7 13.9 13.0 1.04 12.5 13.6  75° 12.1 1.04 11.712.6 13.3 1.05 12.7 13.9  90° 13.2 1.05 12.6 13.8 12.5 1.04 12.0 13.1105° 12.8 1.05 12.2 13.4 12.4 1.04 11.9 12.9 120° 13.1 1.04 12.6 13.712.4 1.04 11.9 12.9 135° 13.3 1.04 12.7 13.9 11.7 1.04 11.3 12.1 150°13.2 1.05 12.7 13.8 11.8 1.04 11.4 12.3 165° 12.6 1.04 12.1 13.1 13.11.04 12.5 13.7 E Average of Slope L2/L1 ÷ ×  0° 12.8 1.04 12.2 13.3  15°13.0 1.04 12.4 13.5  30° 12.7 1.04 12.2 13.2  45° 12.7 1.04 12.2 13.3 60° 12.8 1.04 12.3 13.4  75° 12.2 1.04 11.7 12.7  90° 13.3 1.04 12.713.9 105° 13.1 1.05 12.5 13.7 120° 12.5 1.04 12.0 13.1 135° 12.4 1.0412.0 12.9 150° 13.2 1.04 12.6 13.7 165° 13.3 1.04 12.7 13.9

TABLE 25 A B Average Average of Slope L2/L1 ÷ × of Slope L2/L1 ÷ ×  0°5.6 1.01 5.6 5.7 5.2 1.01 5.2 5.3  15° 5.9 1.01 5.8 5.9 5.2 1.01 5.2 5.2 30° 5.4 1.01 5.4 5.5 5.7 1.01 5.6 5.8  45° 5.5 1.01 5.4 5.5 5.4 1.015.4 5.5  60° 5.7 1.01 5.7 5.8 5.6 1.01 5.5 5.6  75° 5.3 1.01 5.3 5.4 5.41.01 5.3 5.4  90° 5.7 1.01 5.6 5.7 5.7 1.01 5.6 5.7 105° 5.8 1.01 5.85.9 5.6 1.01 5.5 5.6 120° 5.7 1.01 5.6 5.8 5.6 1.01 5.5 5.6 135° 5.81.01 5.7 5.8 5.6 1.01 5.5 5.7 150° 5.1 1.01 5.0 5.1 5.7 1.01 5.7 5.8165° 5.5 1.01 5.4 5.5 5.7 1.01 5.7 5.8 C D Average Average of SlopeL2/L1 ÷ × of Slope L2/L1 ÷ ×  0° 5.7 1.01 5.6 5.7 5.7 1.01 5.6 5.7  15°5.8 1.01 5.8 5.9 5.6 1.01 5.5 5.6  30° 5.6 1.01 5.6 5.7 5.4 1.01 5.3 5.4 45° 5.5 1.01 5.5 5.6 5.4 1.01 5.3 5.4  60° 5.2 1.01 5.2 5.2 4.9 1.014.9 5.0  75° 5.7 1.01 5.6 5.7 4.7 1.01 4.7 4.8  90° 5.5 1.01 5.5 5.6 5.41.01 5.3 5.4 105° 5.7 1.01 5.7 5.8 5.8 1.01 5.7 5.8 120° 5.9 1.01 5.86.0 5.5 1.01 5.4 5.5 135° 5.5 1.01 5.5 5.6 5.4 1.01 5.4 5.5 150° 5.41.01 5.4 5.5 5.7 1.01 5.6 5.7 165° 5.4 1.01 5.3 5.4 5.1 1.01 5.1 5.2 EAverage of Slope L2/L1 ÷ ×  0° 5.3 1.01 5.3 5.4  15° 5.6 1.01 5.5 5.7 30° 5.2 1.01 5.1 5.2  45° 5.5 1.01 5.5 5.6  60° 5.5 1.01 5.5 5.6  75°5.8 1.01 5.7 5.8  90° 5.4 1.01 5.3 5.4 105° 5.2 1.01 5.1 5.2 120° 5.41.01 5.3 5.4 135° 5.1 1.01 5.0 5.1 150° 5.8 1.01 5.7 5.8 165° 5.1 1.015.1 5.1

TABLE 26 A B Average Average of Slope L2/L1 ÷ × of Slope L2/L1 ÷ ×  0°19.5 1.10 17.8 21.5 19.8 1.10 18.0 21.7  15° 19.0 1.10 17.4 20.8 19.31.10 17.6 21.2  30° 19.2 1.10 17.5 21.0 19.3 1.10 17.6 21.2  45° 19.11.09 17.4 20.9 19.0 1.09 17.4 20.8  60° 19.8 1.10 18.0 21.8 19.7 1.1017.9 21.7  75° 19.1 1.10 17.4 20.9 19.2 1.10 17.5 21.0  90° 19.5 1.1017.8 21.5 19.4 1.10 17.7 21.3 105° 19.5 1.10 17.7 21.4 19.6 1.10 17.821.6 120° 19.1 1.09 17.4 20.9 19.8 1.10 18.0 21.7 135° 19.4 1.10 17.721.3 19.5 1.10 17.7 21.5 150° 19.5 1.10 17.7 21.4 18.9 1.09 17.3 20.7165° 19.4 1.10 17.7 21.3 19.5 1.10 17.8 21.5 C D Average Average ofSlope L2/L1 ÷ × of Slope L2/L1 ÷ ×  0° 19.3 1.10 17.6 21.1 19.2 1.1017.5 21.0  15° 19.2 1.10 17.5 21.0 19.9 1.10 18.1 22.0  30° 19.3 1.1017.6 21.1 18.9 1.09 17.3 20.7  45° 19.4 1.10 17.7 21.4 19.5 1.10 17.721.4  60° 19.6 1.10 17.8 21.6 19.6 1.10 17.8 21.6  75° 19.4 1.10 17.721.4 19.7 1.10 17.9 21.7  90° 19.4 1.10 17.7 21.3 19.7 1.10 17.9 21.7105° 19.4 1.10 17.7 21.4 19.3 1.10 17.7 21.2 120° 19.5 1.10 17.7 21.419.8 1.10 17.9 21.8 135° 19.4 1.10 17.7 21.3 19.6 1.10 17.8 21.5 150°19.8 1.10 18.0 21.9 19.6 1.10 17.8 21.6 165° 19.5 1.10 17.7 21.4 19.51.10 17.8 21.5 E Average of Slope L2/L1 ÷ ×  0° 20.3 1.11 18.3 22.5  15°19.6 1.10 17.9 21.6  30° 19.3 1.10 17.7 21.2  45° 18.8 1.09 17.2 20.6 60° 19.0 1.09 17.4 20.8  75° 19.3 1.10 17.6 21.2  90° 19.4 1.10 17.621.3 105° 19.0 1.10 17.4 20.9 120° 20.3 1.11 18.4 22.4 135° 18.9 1.0917.4 20.7 150° 19.0 1.09 17.4 20.8 165° 19.0 1.09 17.4 20.8

As it is clear from Tables 23-26, the average of absolute values ofslope of comparative examples are 20° or higher and 75° or lower in alldirections at all measurement points or in some directions at allmeasurement points.

Then, the light control films of Comparative examples 1-4 wereincorporated into a 15-inch edge-light backlight (one cold cathode raytube each on upper and lower positions) as in examples of embodiment1-3, and placed on a light guiding plate so that the rough surfacepatterned surface of the film becomes a light emerging surface tomeasure a luminance distribution (emergent angle distribution) inhorizontal direction ±45° and in vertical direction ±45°. Resultsmeasured at points A-E are shown in Tables 27-30. An averages of allmeasurements (θ_(ave), Lr, θ_(ave)/Lr, θ_(ave)×Lr) at 5 points A-E areshown together with the values of haze measured by using a haze meter(HGM-2K: Suga Shikenki) in Table 31. The unit of the figures in thetable is cd/m². Further, a distribution of luminance in horizontal andvertical directions at point C in the backlight in the Comparativeexample 1 is shown in FIG. 17.

TABLE 27 A B C D E Horizontal L45° 2040 2030 2320 2050 1980 DirectionL30° 2170 2150 2480 2150 2090 0° 2080 2080 2380 2020 2030 R30° 2160 21602490 2100 2140 R45° 2020 2030 2310 1970 2060 Vertical U45° 115 111 144145 153 Direction U30° 1600 1610 2230 3240 3250 0° 2080 2080 2380 20402030 D30° 3280 3270 2210 1510 1510 D45° 159 156 152 121 117

TABLE 28 A B C D E Horizontal L45° 1190 1140 1450 1190 1170 DirectionL30° 1210 1180 1450 1200 1190 0° 1140 1130 1350 1140 1130 R30° 1190 12001450 1200 1210 R45° 1150 1200 1450 1170 1200 Vertical U45° 1180 11701790 2600 2580 Direction U30° 1150 1150 1660 1970 1960 0° 1140 1130 13501140 1130 D30° 1930 1940 1620 1090 1080 D45° 2570 2580 1740 1110 1120

TABLE 29 A B C D E Horizontal L45° 1100 1050 1380 1110 1100 DirectionL30° 1060 1030 1290 1060 1050 0° 997 993 1190 980 986 R30° 1030 10201290 1060 1050 R45° 1060 1060 1370 1090 1120 Vertical U45° 1140 11301780 2590 2630 Direction U30° 1020 1030 1520 1740 1750 0° 997 993 1190980 986 D30° 1700 1680 1460 968 973 D45° 2510 2530 1700 1060 1040

TABLE 30 A B C D E Horizontal L45° 1100 1080 1300 1120 1090 DirectionL30° 1440 1400 1700 1440 1410 0° 1480 1490 1720 1470 1480 R30° 1410 14401700 1420 1430 R45° 1080 1110 1300 1080 1120 Vertical U45° 1090 10801480 2020 2010 Direction U30° 1370 1380 1920 2340 2350 0° 1480 1490 17201470 1480 D30° 2350 2340 1880 1310 1300 D45° 2000 2010 1480 1030 1050

TABLE 31 Haze av. slope Lratio θ ave/Lr θ ave * Lr Comparative 91.8 28.41.21 23.4 34.6 Example 1 Comparative 91.8 12.8 1.04 12.2 13.3 Example 2Comparative 56.0 5.5 1.01 5.4 5.5 Example 3 Comparative 95.7 19.4 1.1017.7 21.3 Example 4

As the results in Tables 28-30 indicate, a good front luminance couldnot be attained as compared with that in Examples of the invention(Tables 11-15 and Tables 20-22) when a conventional light diffusionsheet was incorporated in the backlight.

Further, the results in Table 27 show that while the luminance changesgreatly depending on direction according to the orientation ofunevenness in case of a prism sheet, the light control films in Examplesof the invention have a relatively uniform luminance distribution and aproper light diffusion property. Further, as the results in FIG. 16 andFIG. 17 indicate, the light control films of Example of the inventionhave a high luminance within the angle of 40° and produced emergentlight in the front direction equal to or higher than that produced by aprism sheet.

Further, if a prism sheet prepared in the Comparative example and pluralnumber of and light diffusion sheets are incorporated in combination inthe backlight, the front luminance equal to that of Examples of theinvention maybe obtained. However, this could obviously increase thethickness of the backlight and the associated cost.

As it is evident from aforementioned examples, according to thisinvention, a light control film with a good front luminance and properlight diffusiveness is provided by making the slope and the geometry ofthe rough surface patterns on the light control film satisfy a certainrelationship. Further, by incorporating such light control film in abacklight, a backlight having a high front luminance without occurrenceof glare and interference patterns is provided.

1. A light control film having a rough surface pattern defining, foreach cross-section perpendicular to a base plane of the film, a profilecurve along an edge contoured by the rough surface pattern, wherein forsubstantially all cross-sections perpendicular to a base plane of thefilm the profile curve has an average of absolute values of slope tosaid base plane θ_(ave) and has a ratio Lr=L2/L1 of the length L2 ofsaid profile curve to the length L1 of a straight line defined byintersection of said base plane and the cross-section satisfy thefollowing:θ_(ave) ÷Lr≧20 and_(25≦)θ_(ave) ×Lr≦60.
 2. A backlight device comprising a light guidingplate, at least one light source located at an edge thereof, said lightguiding plate having a light emergent surface approximately orthogonalto said edge, and a light control film according to claim 1 located onthe light emergent surface of said light guiding plate.
 3. A backlightdevice comprising a light control film according to claim 1, a lightsource, and a light diffusing material between said light source andsaid light control film.
 4. A light control film including a surfacelayer of a material having a refractive index n, said surface layerhaving a rough surface pattern defining, for each cross-sectionperpendicular to a base plane of the film, a profile curve along an edgecontoured by the rough surface pattern, wherein for substantially allcross-sections perpendicular to a base plane of the film, the profilecurve has an average of absolute values of slope of the profile curve tosaid base plane θ_(ave) and has a ratio Lr=L2/L1 of the length L2 ofsaid profile curve to the length L1 of a straight line defined by theintersection of said base plane and the cross sections satisfy thefollowing Formula:θ_(ave) ÷Lr×n ²≧40 and50 ≦θ_(ave) ×Lr×n ²≦135.
 5. A backlight device comprising a lightguiding plate, at least one light source located at an edge thereof,said light guiding plate having a light emergent surface approximatelyorthogonal to said edge, and a light control film according to claim 4located on the light emergent surface of said light guiding plate.
 6. Abacklight device comprising a light control film according to claim 4, alight source, and a light diffusing material between said light sourceand said light control film.